tm ( sec) ~ 10-6 / P (0.2)
where P is the pressure in mbar.
what is the physical interpretation of this?
Evaporation deposition is performed under high vacuum conditions in order to obtain a
desired level of purity of the thin films. In working with a vacuum, pressures are usually
measured in mbar (the conversion to the CI unit is 1 mbar = 100 Pa. The impingement rate
(Ri) of residual gases as calculated from the kinetic theory is proportional to pressure :
Ri = P/ Square root of (2 (Phi)(m)(T))
where m is the particle mass, k is the Boltzmann constant and T is the temperature.
The impingement rate suggests the question: "how do you estimate the monolayer adsorption
time of a residual gas?" That time is:
tm ( sec) = 10 ^(-6) / P (0.2)
where P is the pressure in mbar.
At a chamber pressure P of 10^-6 mbar, the allowed deposition time of a film on a clean surface before that surface becomes substantially contaminated with residual gas is about 1 second
rEF: www.tf.uni-kiel.de/servicezentrum/neutral/praktika/.../m101.pdf
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